1. Field of the Invention
The present invention relates to a wire bonding structure used for e.g. a semiconductor device. The present invention also relates to a semiconductor device including the wire bonding structure. The present invention further relates to a wire bonding method, and a bonding tool used for the method.
2. Description of the Related Art
FIGS. 15 and 16 show an example of wire bonding method using a conventional bonding tool (see JP-A-2006-114649, for example). As shown in FIG. 15, the bonding tool 90 includes a wedge 91, a wire guide 92 and a cutter 93. The wedge 91 is supported by a horn (not shown) for supplying ultrasonic vibration. The wire guide 92 serves to guide a wire 96 to the end of the wedge 91. The wedge 91 applies ultrasonic vibration under pressure to the wire 96 sandwiched between the end of the wedge 91 and a bonding target, whereby the wire 96 and the bonding target are bonded together. Thereafter, the wire 96 is cut with a cutter 92.
In the above-described wire bonding method, as shown in FIG. 15, a semiconductor element 98 is first mounted on a lead 97A, and then first bonding is performed with respect to the electrode pad 98a of the semiconductor element 98. Specifically, wedge 91 applies ultrasonic vibration to the wire 96 while pressing the wire 96 against the electrode pad 98a. This process allows the wire 96 to be bonded to the electrode pad 98a, whereby the first bonding portion 96A shown in FIG. 16 is provided. Then, second bonding is performed with respect to a pad portion 97Ba of the lead 97B. Specifically, as shown in FIG. 16, the bonding tool 90 is moved to a position directly above the lead 97B. Then, the wedge 91 applies ultrasonic vibration to the wire 96 while pressing the wire 96 against the pad portion 97Ba. This process allows the wire 96 to be bonded to the pad portion 97Ba, whereby the second bonding portion 96B is provided.
To prevent the wire 96 from becoming separated from the electrode pad 98a, it is desirable to make the first bonding portion 96A large. To achieve this, the wedge 91 needs to be made large, and accordingly, the pad portion 97Ba for the second bonding needs to be made large. However, an increase in size of the pad portion 97Ba is disadvantageous for the size reduction of the entire semiconductor device.